A population which belongs to the same organism species, but has a different character from that of other population in a certain character due to different genetic construction is called variety (cultivar). That is, even the same kind of plant is different in difficulty of culturing, pest resistance, yield, quality or the like, depending on a cultivar. For this reason, in agricultural crops, particularly, main crops such as rice and wheat, cultivar improvement for obtaining a more excellent cultivar has been conducted from old times. In recent years, this cultivar improvement has been positively conducted in not only seed and plant suppliers but also public organizations such as country and prefecture. In addition, in order to response to variety of taste of consumers in recent years, in horticultural crops such as grasses and flowers in addition to edible crops, a new cultivar having a variety of colors and morphologies is vigorously being developed.
Further, in recent years, an attention is paid to a plant source as a raw material such as biomass ethanol and the like, and development of a new cultivar having high source efficiency is expected.
With advance of nucleic acid analysis technique or the like in recent years, genes of a variety of plants such as Arabidopsis, rice, wheat and the like have been analyzed, and genetic information obtained by this analysis has been disclosed. Utilizing the disclosed genetic information, cultivar improvement of introducing a foreign species gene into an original cultivar by a gene recombinant method is performed frequency. For example, a Hd1 gene encoding a protein derived from a plant having the function of increasing photosensitivity of a plant, and a method of creating a transformed plant with this Hd1 gene introduced therein, and the like are disclosed (see, for example, Patent document 1). However, although cultivar improvement by a gene recombinant method has an advantage that a character possessed by a distant species which cannot be usually mated can be introduced, there is a problem that study of safety thereof is not necessarily sufficient.
On the other hand, as a method of improving a plant cultivar by a non-gene recombinant method, there are a breeding method by mating and a mutation method. As a breeding method by normal mating, there is a pedigree breeding method, a population breeding method, a backcross breeding method and the like. Alternatively, by combining the backcross breeding method and MAS (Marker Assisted Selection) method, cultivar improvement of introducing a target gene into an original cultivar is also widely performed. Herein, the MAS method is a method of selecting an individual having an objective character from a population of a cross progeny obtained by natural mating which has been conducted from old times or artificial mating using a DNA marker linked to a gene encoding an objective character. By performing individual selection using this DNA marker, an individual having an objective character can be selected at an early stage such as a seedling stage and the like, and it can save labor and improve efficiency. As a method of selecting an individual having a particular character using such the DNA marker, for example, a method of determining a genotype of a plant using a DNA marker present in a region surrounding a sd-1 gene which is a rice semidwarf gene, and a method of testing semidwarf character of a plant using this method are disclosed (see, for example, Patent document 2).